1. Field of the Invention
The present invention relates to an apparatus for controlling a rotational phase, and in particular to an apparatus for controlling a rotational phase which may be used to control a valve timing of an automotive engine.
2. Description of the Related Art
Conventionally, an apparatus for controlling a rotational phase of an output member with respect to an input member is, for example, used to control a valve timing of an automotive engine. The engine is provided with a valve driving mechanism in which an engine rotation is transmitted through a transmitting means by a crankshaft to a camshaft and intake valves and exhaust valves are driven by the camshaft so as to open or close. In this case, a rotational phase control apparatus is installed between an input member or a cam pulley connected with a crankshaft and an output member or the camshaft.
Such rotational phase control apparatus is, for example, disclosed in Japanese patent unexamined publication No. 4-232312. The apparatus in this patent publication is provided with a planetary gear mechanism between a camshaft and a cam pulley. The planetary gear mechanism is provided with a sun gear, planet gears supported by a planetary carrier, and a ring gear. The ring gear is connected with the cam pulley, and the planet carrier is connected with the camshaft. Further, the sun gear is connected with a sleeve at whose rear end a driving force receiving gear is installed. On the other hand, an engine body is provided with a step motor and the shaft of the step motor is provided with a worm thereon to mesh with the driving force receiving gear.
In the above-mentioned apparatus, when the sun gear is stopped, the camshaft rotates with a constant speed reducing ratio with respect to the cam pulley. When the sun gear is driven through the worm or the like by the step motor, the phase of the camshaft is shifted.
In the conventional apparatus mentioned above, the planetary gear mechanism is installed on the end of the camshaft, and the motor is located such that the shaft of the motor extends vertically to the camshaft. The worm provided on the motor shaft is meshed with a relatively large gear which is provided on the rear end of the sleeve connected with the sun gear of the planetary gear mechanism. Therefore, some problems exist in the conventional apparatus. Namely, it is complicated to install the motor and the like. Further, since a space for the installment of the step motor, the worm and the like is necessary in the side portions of the camshaft, it is difficult for the driving mechanism of the valves including the rotational phase control apparatus to be downsized.